2004 GMC ENVOY

Typical onset: 120,000-180,000 mi

Symptoms: Sudden loss of oil pressure with no external leaks, Severe rod knock or bottom-end noise, Metal shavings in oil during change, Engine seizes or spins bearing without warning

Fix: This engine grenades internally—rod bearings, main bearings, crankshaft damage. Most cost-effective fix is used engine swap (12-16 hours) or short block replacement if heads are good (18-24 hours). Rebuilds rarely make financial sense on these.

Estimated cost: $4,500-7,500

Typical onset: 80,000-150,000 mi

Symptoms: Pink or milky transmission fluid (coolant mixing), Transmission slipping or delayed engagement, Coolant loss with no visible leaks, Strawberry milkshake appearance in radiator or trans pan

Fix: The internal trans cooler in the radiator fails, allowing coolant and ATF to mix—kills the transmission. Requires radiator replacement, trans cooler line flush, transmission flush or full rebuild if contamination went unnoticed (rebuild adds 14-18 hours). Catch it early and you're looking at radiator and flush only (4-5 hours).

Estimated cost: $800-1,200 (early catch); $3,500-5,000 (with trans rebuild)

Typical onset: 100,000-160,000 mi

Symptoms: White smoke from exhaust on startup, Coolant consumption with no external leaks, Overheating or erratic temp gauge, Oil looks like chocolate milk

Fix: The 4.2L I6 blows head gaskets—often both banks simultaneously. Both heads need removal, decking, and gasket replacement. Budget 16-20 hours labor. While you're in there, replace water pump, thermostat, and any suspect coolant hoses.

Estimated cost: $2,800-4,200

Typical onset: 70,000-130,000 mi

Symptoms: Clunk or thud during shifts (P to D, D to R), Vibration at idle in gear, Excessive driveline movement visible under throttle, Banging noise over bumps from transmission area

Fix: Transmission mount fails—rubber separates from metal bracket. Easy replacement (1.5-2 hours) but often ignored until it damages crossmember or exhaust. Inspect engine mounts at same time; they fail similarly.

Estimated cost: $250-450

Typical onset: 90,000-140,000 mi

Symptoms: Check engine light P0442 or P0446 (EVAP small leak), Fuel smell near tank or filler area, Hard starting when hot or after sitting, Intermittent stalling or loss of power

Fix: EVAP vent valve solenoid and fuel tank pressure sensor fail regularly. Fuel pump itself is known to quit without warning. Pump replacement requires tank drop (3-4 hours). EVAP components are easier (1-2 hours) but require smoke test to confirm.

Estimated cost: $400-700 (EVAP parts); $800-1,200 (fuel pump)

Typical onset: 80,000-150,000 mi

Symptoms: Gear oil drips on garage floor (front of engine area), Whining noise during turns or acceleration, Clunking when engaging 4WD, Burning oil smell after highway driving

Fix: Front diff and transfer case seals leak. If fluid runs low unnoticed, internal damage occurs (bearings, gears). Seal replacement is 2-3 hours; full rebuild is 8-12 hours. Check fluid level every oil change on these.

Estimated cost: $400-800 (seals); $2,000-3,500 (rebuild)

Typical onset: null

Symptoms: Window switches intermittent or dead, Door locks cycle randomly or fail to unlock, Gauge cluster lights flicker or go dark, Blower motor works only on high speed

Fix: Typical GM switch and module failures. Window switch replacement is 0.5 hours; door lock actuators 1-1.5 hours each; cluster repair/replacement 2-3 hours. Blower resistor is a known failure (0.5 hours).

Estimated cost: $150-400 per issue